Photopolymerizing and photocrosslinking compounds have widespread applications in the industry. For example, processes related to coatings, photoresists, lithographic plates and the like are based on such compounds. Photopolymerization and photocrosslinking have been subject of several review articles such as, for example, in Encyclopedia of Polymer Science and Engineering, Volume 4, page 350 (John Wiley & Sons, Inc., New York, 1986) and ibid., Vol. 11, 187 (1988). Generally, photoreactive compositions contain monomers which, under the action of light, polymerize (photopolymerization) or crosslink when additional monomers are present (photocrosslinking). They may also crosslink on their own if they are multifunctional. A photoinitiator (or photosensitizer) is generally used in such reactions, although it is not always necessary.
Photopolymerizable compositions as used at present contain polymerizable monomers such as, for example, esters of acrylic or methacrylic acid, particularly those of acrylic acid with polyhydric aliphatic alcohols. Exemplary thereof are the following monomers; hexanediol(1,6)-diacrylates, triethylene glycol diacrylate, polyethylene glycol diacrylate, neopentyl glycol diacrylate, diglycerol diacrylate, trimethylol propane triacrylate, pentaerythritol tetraacrylate, and dipentaerythritol penta-and hexa-acrylate,
There are several deficiencies associated with such monomers in the presently known photoreactive systems. For example, triethylene glycol diacrylate, trimethylol ethane triacrylate and trimethylol propane triacrylate, have undesirably high volatility. Monomers such as pentaerythritol tetraacrylate are solid at room temperature and crystalize in the photopolymer layer, thus affecting film quality. Furthermore, in case of monomers such as, for example, pentaerythritol triacrylate and dipentaerythritol penta- and hexaacrylates, unwanted monomer migration typically occurs in photopolymerizable systems, again affecting the usefulness of such systems.
Thus, there is a need in the industry for monomers that have high photoreactivity, sufficiently low vapor pressures, a viscous fluid character, as well as low susceptibility for monomer migration.
European Patent Application number 91300706.8 (Minnesota Mining and Manufacturing Company) discloses polymeric compositions containing halomethyl- 1,3,5-triazine moieties for photosensitive applications, to tackle migration problems. It would, however, be useful if monomer systems which have the desired properties are available since the additional polymerization step can be avoided.
It is therefore an object of the present invention to provide new photopolymerizable monomers which are highly photoreactive and can be used as an integrated component in photopolymerizable and photocrosslinkable coating systems.
It is a further object of the present invention to provide improved photocrosslinkable coating systems with minimal migration of monomer to the interfaces.
It is another object of the present invention to provide an improved multilayer color proofing system with the novel monomers of this invention incorporated in such system.